tains a fauna transitional in fades between that typical of 

 the California Province proper on one hand and that of the 

 Mexican Province on the other, and is therefore an excellent 

 example of the resultant of the mingling of two dissimilar 



units. 



SYNOPSIS OF SPECIES.- 



References marked with an asterisk refer to figures, records to 

 the original locality. 



UNIONIDAE. 



Anodonta cygnea (Linne.) 



Mytilus cygneus Linne. Sys. Nat. '10 ed.), 1758. 1. 706; 

 Anodonta Oregonensis Lea, Trans. Am. Phil. Soc. VI, 1838, 80, 

 PL XXI, 67; *A. cygnea Hannibal. W. Coast Shells, 1910, 302, 

 PL II, 7. 



The region under discussion is several hundred miles south 

 of the existing range of typical Anodonta cygnea. The species 

 is found, however, in an artificial pond in one of the Los 

 Angeles parks, whither it was doubtless introduced in the 

 glochidium stage on fish from Oregon or Washington, some 

 years ago. The record is an interesting one since it illustrates 

 the chief mode of distribution of this group. 



All Europe, Siberia: Pacific drainage of North America 

 south to latitude of Mount Shasta. California, infrequently in 

 Great Basin and middle California. 



Los Angeles System: artificial pond, Eastlake Lark. Los 

 Angeles ill. Hemphill) tide Keep. (II Hannibal . 



Anodonta cygnea impura i Say). Fig. III. 



Anodonta impura Saw New Harm. Diss. II. 1829, 355; 

 A. Nuttalliana Lea Trans'. Am. Phil. Soc. VI. 77. PL XX. (i-L 

 A. Wahlamatensis Lea, Loc. cit. 18:58. 78. PL XX: 64: A. Cali- 

 forniensis Lea. Trans. Am. Phil. So.-. X. 1852, 286, PL XXV, 

 17; A. cygnea impura Hannibal. W. Coast Shells. 1910, 30o 

 (fig. not typical I. 



This well known Naiad, locally common in the few peren- 

 nial streams and ponds of southern California, has passed in 

 the literature under a variety of names, all of which have been 

 duly considered and the earliest, applied by the father of 

 American conchology, Thomas Say. to specimens which he ob- 

 tained from the suburbs of Mexico City while on a horseback 

 trip to that then conchological terra incognita in the early 

 years of the last century, has been retained in the new edition 

 of West ( oast Shells. 



It is unfortunate that the records of Anodonta from 

 southern California are few. The draining of ponds and 

 lagoons and the use of river waters for irrigation so threaten 

 to exterminate it that in a few years it will be almost impossible 

 to obtain an adequate idea of its former distribution. 



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